1. Field of the Invention
This invention relates to a copper alloy which is adapted for use as terminals, connectors, wire harnesses and the like. More particularly, the invention relates to a copper alloy which is suitably employed for general and industrial purposes and also for automobiles and is excellent in stress relaxation resistance characteristic and peeling off resistance of solder. The invention also relates to a method for making such an alloy.
2. Description of Related Art
For the purposes mentioned above, there have been hitherto used copper alloys including brass, phosphor bronze and the like. However, a recent trend toward the miniaturization of terminals and connectors needs electrical conductivity and strength higher than those of brass and phosphor bronze. Moreover, as pitches between pins of parts become narrower, there has arisen the problem that migration takes place. It will be noted that the term "migration" used herein means short-circuiting which is caused by bringing about moisture condensation between electrodes to ionize an metallic element of the electrode, migrating the ionized metallic element toward a cathode by the action of the Coulomb's force and depositing the element thereon, and causing metal deposits to be grown from the cathode in a dendritic form, like plating (electrodeposition), thereby arriving at the anode side.
In order to cope with this situation, Japanese Laid-open Patent No. 62-199741 proposes a Cu--Sn--Ni--P alloy which has good strength and good migration resistance and which can suppress stress corrosion cracking from occurring. However, with terminals and connectors, which are employed for general and industrial purposes and mounted on automobiles (especially around engines), the temperature on their use arrives at about 150.degree. C. Thus, it is strongly required to improve strength under high temperature conditions, and particularly, to keep spring characteristics and improve a stress relaxation characteristic. However, when using conventional manufacturing methods, such requirements have not been met satisfactorily.
The alloy proposed in Japanese Laid-open Patent Application No. 62-199741 is a precipitation hardening alloy, and a batch (2 hours) step is adopted for intermediate annealing, thus inviting the formation of phosphides. Such long-time annealing leads to non-efficiency in productivity, thus resulting in the cost rise.